what should be paid attention to when drawing PCB diagram from the welding angle（2）

Factors affecting PCB welding quality

From PCB design, all components welding to a high-quality circuit board, there is a need for strict control of the PCB design engineer and even the welding craft, the level of the welding workers. The main factors: PCB diagram, quality of the board, quality of the device, oxidation degree of the device pins, quality of the solder paste, printing quality of the solder paste, accuracy of the SMT machine, and mounting quality of SMT machine , the setting of the temperature of the reflow oven, and so on.

Advice for PCB layout

9.Place the device not to rotate at any angle

Since the SMT machine cannot rotate at any angle, it can only rotate 90 ° C, 180 ° C, 270 ° C, 360 ° C. Otherwise it will affect the welding quality.

10.Should pay attention to the problem when the adjacent pins are shorted

As long as each pin is not connected, the chip has no short circuit and looks good in appearance.

11. On the bottom of the chip the problem of the middle pad.

If the chip in the middle of the chip has a pad, if the pad in the middle of the package is printed, it is easy to cause a short circuit. It is recommended to shrink the middle pad to increase the distance between it and the surrounding pin pads, thus reducing the chance of a short circuit.

12. The two devices with higher thickness should not be closely packed together.

If they are tightly packed together, it will cause the SMT machine to touch the previously attached device when the second device is mounted. The machine will detect the danger and cause the machine to automatically power off.

13.About BGA

Because the BGA package is special, its pads are under the chip, and the welding effect is not visible outside. For ease of repair, it is recommended to place two Hole Size: 30 mil locating holes on the PCB to position the stencil (for solder paste) during rework.

The size of the positioning hole should not be too large or too small. It is better to make the needle not to be dropped, not shaken, and a little tight when the needle is inserted. Otherwise, the positioning is not accurate. It is also recommended to leave a space in a certain area around the BGA to place the device so that the soldering paste can be placed under the stencil.

14. About the PCB board color

It is not recommended to make in red. Because the red circuit board is white under the red light source of the camera of the SMT machine, it cannot be programmed, and it is not convenient for the SMT machine to perform welding.

15. About small devices under large devices

Some people like to place small devices under the same large device, such as: under the digital tube, there is a resistor.

Such layout will cause difficulties in rework, and it is necessary to disassemble the digital tube before rework, and it may cause damage to the digital tube. It is recommended to discharge the resistor under the digital tube to the Bottom surface.

16.On the copper and the pad connect to affect the melting tin

Since the copper coating absorbs a large amount of heat, it is difficult for the solder to be sufficiently melted to form virtual welding.

The device welding pad is directly connected to the copper, and a large area of copper is coated, which will cause the solder paste to not be sufficiently melted due to the large amount of heat absorbed by the copper; therefore, it is recommended that the pad be isolated from the large area of copper.

Hopefully the knowledge shared above is helpful to you